It is important in road construction that the road surface applied by road finishers, such as, for example, asphalt material, is subsequently compacted by road rollers. For this, during operation one or several road rollers move in an area preset by one or several road finishers in which asphalt material has been deposited. Road rollers and road finishers form an operating unit and usually remain close to one another on the construction site.
In order to sufficiently compact the asphalt material, every region of the road is passed several times by a roller. The number of passings is of particular importance for the quality. In order to be able to determine the number of passings, the position of the road roller for different points in time is necessary. When the position and the speed of the road finisher are known, it is sufficient to determine the position of the road roller relative to the road finisher.
Determining the position of a mobile object by means of transponders at fixed locations of known positions is described in WO-A-2005/015257 and a determination of the number of times the roller passes over road sections is given in U.S. Pat. No. 5,942,679.